1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such physiological characteristics. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modem medicine.
One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the “pulse” in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle.
Pulse oximeters typically utilize a non-invasive sensor that transmits light through a patient's tissue and that photoelectrically detects the absorption and/or scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms.
Conventional pulse oximetry sensors are either disposable or reusable. In many instances, it may be desirable to employ, for cost and/or convenience, a reusable pulse oximeter sensor. Reusable sensors are typically semi-rigid or rigid devices that may be clipped to a patient. Unfortunately, reusable sensors may be uncomfortable for the patient for various reasons. For example, sensors may have angled or protruding surfaces that, over time, may cause discomfort. In addition, reusable pulse oximeter sensors may pose other problems during use. For example, lack of a secure fit may allow light from the environment to reach the photodetecting elements of the sensor, thus causing inaccuracies in the resulting measurement.
Because pulse oximetry readings depend on pulsation of blood through the tissue, any event that interferes with the ability of the sensor to detect that pulsation can cause variability in these measurements. A reusable sensor should fit snugly enough that incidental patient motion will not dislodge or move the sensor, yet not so tight that normal blood flow to the tissue is disrupted. As sensors are worn for several hours at a time, an overly tight fit may cause local exsanguination of the tissue around the sensor. Exsanguinated tissue, which is devoid of blood, shunts the sensor light through the tissue, resulting in increased measurement errors.